1. Field of the Invention
The present invention relates to a lumbar support device for use in an automotive seat.
2. Description of Prior Art
Among various conventional lumbar support devices provided in an automotive seat, there has been known the one of the type wherein a lumbar support plate is rockably supported on a free end of a support arm whose base end is pivoted to a base bracket in a rotatable way, so as to adjustably support the lumbar part of an occupant sitting on the seat. In most instances, such device includes a spring biasing member provided between a cam and the base end of a support arm, the cam being operatively connected with an operation lever exposed on the lateral wall of the seat back of the seat, so that the lumbar support plate is resiliently biased toward the occupants' lumbar part by the biasing force of the spring member.
The lumbar support plate is so arranged within the seat back that the plate is disposed at a location corresponding to the occupants' lumbar part and closer to the occupant than other elastic support members as sinuous springs which elastically supports the cushion member of the seat back.
Thus, in such construction, the lumbar support plate is displaced forwardly and backwardly relative to the seat back, by operating the lever to change discrete cam surfaces of the cam to vary the biasing force of the spring biasing member. This adjustment is made, depending on the degree of the load being exerted upon the lumbar support plate from the occupant.
However, a defective aspect is found in this kind of conventional device, in that the forward projection of the lumbar support plate, more than the sinuous springs, results in increasing the thickness of the seat back on the whole, and creating variations in the outer configuration of the seat back as well as the cushioned surfaces thereof. Consequently, it has been difficult to produce a number of seats having the same configurations in a uniform way. Further, such irregularities in seat back configurations, makes a difference over all seat backs produced, whether they are the one containing the lumber support device or the one without it, having unfavorable results in terms of sitting touch and psychological state of occupant sitting on the seat.
In addition, in this device, the forward and backward displacement (stroke) of the lumbar support plate, which is made according to changes in the discrete surfaces of the cam, naturally varies the position of the plate per se against the occupant, with the result that the occupant feels excessively pressed or does not feel sufficient support touch at the lumbar part.